1. Field of the Invention
This invention relates to a radiation three-dimensional position detector including a scintillator unit and a light receiving element.
2. Related Background Art
The radiation three-dimensional position detector is used, for example, in a PET (positron emission tomography) apparatus as a radiation detector which detects pair of γ-ray photons (energy: 511 k eV), which is produced following on the pair annihilation of electron and positron within a subject to which a positron emission isotope (RI radiation source) is applied, and fly in the opposite directions with respect to each other. The PET apparatus detects pair of γ-ray photons with a radioactive transducer in a manner of simultaneous counting, and the simultaneously counted information is accumulated to create a histogram. Further, the PET apparatus, reconstructs, based on the created histogram, an image representing spatial distribution of the generative frequency of the pair of γ-ray photons in a measurement space. The PET apparatus performs an important role in the field of nuclear medicine. By using the PET apparatus, for example, function of living organism and high-level function of brain can be examined.
The radiation three-dimensional position detector, which is suitably used as a radioactive transducer for such PET apparatus, includes a scintillator unit and a light receiving element (for example, refer to Patent document 1 and Non-patent document 1). From among the above mentioned scintillator unit and light receiving element, the light receiving element outputs electric signal corresponding to the incident position and intensity of the light incident on the light incident plane. The scintillator unit is disposed on the light incident plane of the light receiving element and includes K layers of scintillator arrays in which scintillator cells for producing scintillation light corresponding to the absorption of the radiation are disposed in two dimensions (K is an integer number of 2 or greater), these K-layers of scintillator arrays are laminated in the direction perpendicular to the light incident plane of the light receiving element.
Particularly, in a radiation three-dimensional position detector disclosed in Patent document 1, the K layers of scintillator arrays are laminated being displaced by 1/K of the disposition pitch of the scintillator cells in the row or column direction. Also, in a radiation three-dimensional position detector disclosed in Non-patent document 1, there are employed scintillator cells having a different fluorescent attenuation constant respectively for the first and third layer scintillator arrays and the second and fourth layer scintillator arrays.
The above-described radiation three-dimensional position detector can detect the position of the radiation absorption in the scintillator unit not only as a location on a two dimensional planes parallel to the light incident plane of the light receiving element but also as a distance from the light incident plane. That is, in the scintillator unit in which a plurality of scintillator cells is disposed in three dimensions, it is possible to determine which scintillator cell has produced the scintillation light based on the position of the barycenter of the scintillation light which has reached the light incident plane of the light receiving element.
[Patent document 1]
Japanese Unexamined Patent Application Publication (Tokukai) No. H-1-229995
[Non-patent document 1]
N. Inadama, et al., “A Depth of Interaction Detector for PET with GSO Crystals Doped with Different Amounts of Ce”, IEEE Transaction of Nuclear Science, Vol.49, No.3, pp.629–633 (2002)